Tamoxifen for Male Breast Cancer

Last Modified: April 30, 2006

Dear OncoLink "Ask The Experts,"

Having had a mastectomy in July 2005, I was prescribed Tamoxifen. I am having difficulty in finding any information on the side effects [of this drug] in men. I appreciate that we are a small number [of all breast cancer patients], but information for breast cancer in men is limited. Can you please advise on any side effects of Tamoxifen in men?

Tamoxifen is generally accepted as the standard of care for adjuvant systemic hormonal therapy (that is, therapy given in addition to local treatment, such as surgery and/or radiation) in breast cancer. Tamoxifen improves survival rates in women with estrogen receptor-positive cancer, and since male breast cancer is hormone receptor-positive in about 90% of cases, hormonal therapy in men makes sense. There are few, if any, randomized clinical trials that have assessed tamoxifen use in men. However, several retrospective studies (which look back on patient records) have compared outcomes, and these found significant benefit to therapy. In one study, the 5-year survival rate (39 male patients with stage II and III disease) was 61%, compared with 44% in men not taking tamoxifen. In the available studies, men received tamoxifen for only 1 to 2 years. Since we know that trials in women have shown the optimum length of tamoxifen therapy to be 5 years, we may actually be underestimating the benefit of tamoxifen in men, as it might be even better if taken for 5 years.

A recently published trial looked at 135 cases of male breast cancer, 38 of whom received hormonal therapy (some also received chemotherapy). Thirty-five of these patients received tamoxifen. Overall, the study found a 51% lower risk of recurrence in men who received tamoxifen versus those who did not. With almost 14 years of follow up, this study found a 55% lower risk of death in those men who took tamoxifen.

The toxicities of tamoxifen in men have not been well studied, but one researcher followed 24 men on tamoxifen and found the following side effects. The most common was a decrease in libido or sex drive, which occurred in 7 patients (or 29.2%); followed by weight gain (6 pts. or 25%); hot flashes (5 pts. or 20.8%); mood alterations (5 pts. or 20.8%); depression (4 pts. or 16.6%); insomnia (3 pts. or 12.5%); and deep venous thrombosis (blood clots)(1 pt. or 4.2%). Five (20.8%) patients stopped therapy with tamoxifen in less than 1 year because of these side effects. Of these patients, 2 had decreased libido, two had hot flashes, and one suffered deep venous thrombosis. In contrast to female patients, in which 4% stop therapy due to side effects, men stop therapy at a rate of 20.8%, according to this study.